In sensor array systems, such as forward-looking sonar systems, or similar type systems, the signals returned from candidate targets include both strong and weak return signals. Strong signals are typically processed by the sensor array without much problem. However, the weak target signals returned from the target have a low average signal amplitude and are typically very noisy, e.g., weak return sonar target signals from undersea mines are often very noisy due to the complicated undersea environment. In order to detect candidate targets from weak noisy return signals, pre-processing is often performed prior to detection to reduce the noise. Some conventional methods to reduce the noise of weak target signals use a technique known as signal subspace projection. Conventional signal subspace processing techniques are typically based on the assumption that the return target signals have greater energy than the noise of the return signals. However, for weak target signals, this assumption is typically not correct. The result is conventional signal subspace projection pre-processing techniques are often not effective at reducing noise which reduces the ability of the sensor array system to detect candidate targets.
Additionally, many conventional thresholding techniques which rely on the threshold amplitudes of signals to determine the location of candidate target assume the noise of the return signals is Gaussian distributed. However, in many applications, such as undersea mine detection, the noise is both Gaussian and non-Gaussian distributed. The result is conventional thresholding techniques do not always detect candidate targets and often generate a lot of false target signals. Moreover, non-Gaussian distribution of the noise is very difficult to estimate and requires extensive computational efforts. Thus, non-Gaussian distribution estimation is rarely, if ever, utilized by conventional thresholding techniques.
Current sensor array systems, such as forward-looking sonar systems, and the like, require the individual sensors of the array to be located in very close proximity to each other due to the physical limitation of the size of the array. Such a configuration often results in a target signal contacting several adjacent sensors simultaneously. This results in a correlation between the target signals received by various sensors of the array, referred to herein as cross-sensor correlations. The inventor hereof has discovered a new method for enhancing weak target signals which exploits such cross-sensor correlations.